Method of and machine for screening pulp



Oct. 31, 1933. J. HAUG 1,932,663

METHOD OF AND MACHINE FOR SCREENING PULP Filed Nov. 8, 1930 2 Sheets-Sheet 1 NVE TOR w ifia BY 2 ATTOR IIE I' Oct. 31, 1933. A. J. HAUG IETHOD OF AND MACHINE FOR SCREENING PULP Filed Nov. 8, 1930 2 Sheets-Sheet 2 Fig.7

i aiented fict. 31 1933 UETD TATES PATENT OFFICE METHOD OF AND ltIACHINE FOR SCREEN- ING PULP lhis invention relates to pulp screening machines and is a continuation, in part, of my pending application Serial No. 331,178, filed January 9, 1929. It aims particularly to improve the chioiency of such machines and to increase their creening capacity without increasing the power consumption.

The invention will be herein disclosed particularly as embodied in machines of the type shown in my prior Patents Nos. 1,533,419, granted April 14, 1925 and 1,551,953, granted September 1, 1925, although it will be understood that the invention is also applicable to other pulp screening machines. A machine of the construction disclosed in said patents includes a screening drum mounted for rapid rotation in a casing having suitable inlet and outlet connections. Pulp to be screened is delivered to the interior of the screening drum, flows through the screening surface of the drum, and is discharged from the casing, the discharge outlet being provided with a weir or arranged in some other manner to maintain the drum constantly submerged in a body of screened stock. Usually the pulp flows into the drum under a relatively low head and the drum is revolved at a sufiicient peripheral speed to create a very substantial centrifugal force in the body of pulp which urges the pulp through the screen. The coarser materials or tailings which cannot pass through the screen accumulate on its inner surface and are moved along said surface toward a tailings outlet by one or more inclined scrapers. Certain of the coarser constituents of the stock, however, still cling to the inner surface of the screen notwithstanding the action of the scrapers, and tend to form a mat which impedes the screening operation and reduces the capacity of the machine. Essentially the same clogging eifect occurs in other forms of pulp screening machines.

The present invention is especially concerned With these accumulations of coarse stock. It is an important object of the invention to improve both the methods of and the machines for screening pulp with a view to minimizing the difliculties introduced in prior machines by the presence of such accumulations.

The nature of the invention will be readily understood from the following description when read in connection with the accompanying drawings, and the novel features will be particularly pointed out in the appended claims.

In the drawings,

Figure 1 is a vertical, longitudinal, sectional View showing the general organization of a machine embodying features of the present invention;

Fig. 2 is a transverse, vertical, sectional view of a machine very similar to that shown in Fig. 1, and constructed in accordance with this invention, Fig. 3 is a longitudinal, vertical, sectional View through the drum and adjacent parts of the machine shown in Fig. 2;

Fig. 4 is an end view of the machine shown in Fig. 1, illustrating, in section, an outlet arrangement;

Fig. 5 is a sectional perspective view illustrating a different form of deflector plate which may be used;

Fig. 6 is a vertical, transverse, sectional view showing another deflector plate arrangement;

Figs. 7 and 8 are longitudinal and transverse sectional views, respectively, of a modification; and r Fig. 9 is a sectional view illustrating an adjustable deflector.

Referring first to Figs. 1 to 4, inclusive, it will be seen that the machine there shown comprises a stationary casing including end members 2 and 3 and a shell 4. Mounted in the casing is a rotary screening cylinder or drum 5 which is supported by an end piece or head 6, the head being secured fast on a shaft 7 which is mounted in bearings 8 and 9. This mounting permits the rapid rotation of the screening drum, and the shaft '7 has a pulley 10 secured thereto by means of which the machine may be belted to any convenient source of power.

The paper stock or pulp to be screened is conducted into the open end of the drum 5 through an inlet connection or spout 12 which preferably is formed integral with a stationary tailings conduit or chute 14. When the machine is in operation the pulp flows into the drum through the spout 12 under a very low head and the rapid revolution of the screen causes a considerable body of stock in contact with it to re-' volve circumferentially around the screen in a direction generally parallel to the peripheral surface of the screen. A very substantial centrifugal effect thus is created in the body of stock so revolved, and the centrifugalforce so produced urges the pulp through the perforations in the screen.

In this machine the screened pulp finds an exit at one end of the casing through the large chain her or outlet connection 15 provided in the end piece 3, thisoutlet discharging directly into a conduit or box 16 equipped with a Weir 17, the

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height of which may be adjusted to vary the hydraulic head under which the screen works, but always being at a suflicient height to maintain the screen 5 constantly submerged. Or, instead of this arrangement, baffles 18, Fig. 1, may be used in the casing to accomplish essentially the same result, as disclosed in my pending application above referred to. The rate at which the pulp is caused to flow through the screen may be governed by properly controlling the rate of inflow or delivery of the stock of the machine, the speed of revolution of the screening drum, and by suitably adjusting the baflies 18 or the height of the weir 17 over which the screened stock is discharged.

The coarser materials or tailings which collect on the inner surface of the screen are moved along said surface by inclined scrapers 23 and finally are ejected from the screen and discharged through the pipe 14.

The entire organization so far described is substantially like that shown in. my Patent No. 1,551,953 except the baffle construction which is shown in my pending application. For a more complete description of the construction and operation of the machine, therefore, reference should be made to said patent and said application.

While the inclined scrapers 23 are effective in moving the greater part of the tailings along the screening surface toward the tailings outlet, it is nevertheless, impractical to set the scrapers so close to the surface of the screen that the entire accumulation of material which cannot pass through the screening surface will be acted upon by the scrapers. In other words, a slight clearance must, as a practical matter, be left between the extreme outer edges of the scrapers and the inner surface of the screen. When the machine is running a coating or accumulation of coarse constituents of the pulp collects on the' inner surface of the screen where it can only be removed by the scrapers when it builds up to a sufficient degree to collect on the edges of the scrapers. Such an accumulation obviously inter feres with the screening action and reduces the capacity of the machine.

I have found, however, that these accumulations can be dislodged by creating reverse pulsations or impulses in the liquid adjacent to the screen. For this purpose the machine shown is provided with several pulsators or deflectors 24 which may consist of plate having flat outer surfaces and curved inner surfaces to fit against the casing shell 4 or against the supplemental shell or sub-casing 25. Figs. 2 and 3. Such a subcasing sometimes is used to encircle the screening drum, and is held in a fixed position with reference to it by the spacing elements 26, this sub-casing serving to produce a more uniform distribution of the flow of stock through the drum around the entire circumference thereof as explained more fully in my pending application. In both arrangements, however, the deflectors serve to constrict, at intervals, the area through which the revolving body of stock must flow. This results in producing periodical inward impulses or movements of the stock through the screening surface, or, in other words, causes a local and temporary reversal of the flow of the stock through the screening surface in regions opposite the deflectors. Such impulses and reversals serve to dislodge accumulations of stock clinging to the inner surface of the drum. Since each deflector extends substantially the entire length of the screen, the reverse flow which it produces occurs throughout a narrow strip of the screening surface opposite the deflector and extending substantially the entire length of the screen. Also, due to the fact that the screen is revolving, these inward impulses and reverse flows travel along the screening surface of the drum around its entire circumference so that substantially its entire surface is kept relatively clean. In addition to freeing the inner surface of the drum from accumulations of stock too coarse to pass through the screen, these inward impulses or reverse flows are also useful in mov ing such accumulations inwardly far enough to permit the scrapers to act on the dislodged stock. They strike it while it is in a free or floating condition and give it an ejecting movement; that is, a movement laterally along the surface of the drum toward the discharge outlet. It seems probable also that during this action some of the good fibre which should pass hrough the screen and which has adhered to the slivers and coarser fibre is freed, so that a recovery of part of the fibre is effected.

The deflectors shown in Figs. 1, 2 and 3 present substantially flat surfaces to the body of stock which revolves around the screen 5, these flat surfaces being separated from each other by intermediate curved sections of the shell 4 or the sub-casing 2-5, as the case may be. I have demonstrated in practice that this arrangement materially improves the efficiency of the machine and substantially increases the screening capacity without increasing the power consumed.

I have also found that even better results can be produced by cutting off the forward or leading portions of the plates or deflectors abruptly. Plates so constructed are shown at 28 in Fig. 6. A still better form of plate is shown at 30 in Fig. 5, the plate 30 differing from the plate 28 in having a surface 31 presented to the revolving body of pulp which is curved, whereas the corresponding face of the plate 24 is fiat, and also in having a more abrupt face 32 at its forward or leading edge.

The reason for the improved results obtained with these two forms of deflectors as compared to the deflectors 24 shown in Figs. 1, 2 and 3, seems to be that in the latter case when the revolving body of stock comes in contact with the outer surface of one of the deflectors, a relatively gradual increase in pressure is produced on the stock which causes the reverse or inward flow of the stock through the screen. As the stock passes the point of maximum constriction or that at which the surface of the plate is closest to the screen 5, the pressure is relieved somewhat and it decreases gradually with a resultant gradual resumption of outflow. If the forward or leading edge of the plate is cut off sharply, as shown in Fig. 6, the inward or reverse flow of pulp is terminated very abruptly in the neighborhood of said forward or leading edge, and the inward flow is followed immediately by a quick outflow. This action is even more pronounced when the deflector shown in Fig. 5 is used. The arrow in this figure indicates the direction in which the body of pulp moves past the deflector plate. The gradually inclined surface 31 produces a gradual increase in pressure in the stock and creates an inflow of stock through the screen, this inflow being terminated abruptly by the release of the pressure as the stock passes the leading edge 32 of the deflector. The inward impulse or movement of the stock is thus followed by a much ffior abrupt impulse iii the normal or outward direction. By properly shaping the deflector plates the character of both the inward and outward impulses may be varied substantially as desired. r

The number of deflectors used will depend upon the design and requirement of individual machines. I prefer, however, where possible to use at least four of. these deflectors spaced'at ap proximately uniform distances around thecircumference of the drum. The deflectors may be made of either wood or metal, and the particular mariner iritvhich they are mounted in the machine will depend upon the characteristics of individual designs.

Under some circumstances it maybe advisable to use an adjustable deflector or pulsator such, fer example, as that shown in Fig. 9. As there shown the deflector plate 24' is pivoted at 33 to the casing 4, and its forward edge is connected to the casing by a heavy rubber strip 34. A stem 35 pivotally connected to the deflector plate extends through the casing and is provided at its outer end with a hand-wheel 36. A portion of this stem is screw threaded into a non-rotating section of the stem. Consequently, when the hand-wheel 36 is rotated the defiector plate is adjusted inwardly or outwardly, depending upon the direction of such rotation.

In some centrifugal pulp screening machines the screening drum is either stationary or revolves very slowly, and the centrifugal action on the stock is produced by revolving blades closely adjacent to the screening surface either inside or outside of it. Such an arrangement is illustrated in Figs. '7 and 8 and comprises a stationary screening drum 40 mounted in a casing 41. The pulp to be screened flows into the drum through an inlet connection 42, Fig. 7 ,while the screened stock is discharged through the outlet connection 43 and over a weir 44, as in the construction shown in Fig. 4. In this machine the centrifugal action is created by revolving a series of blades, arms or paddles 45 closely adjacent to the inner surface of the screen, these blades or paddles being mounted on a shaft 46 which may be belted to any convenient source of power. The casing 41 includes a reentrant memberfl'l which extends into the drum for nearly its entire length and is provided, with flat external surfaces. The particular construction shown is hexagonal in cross-sectional outline.

As the blades or paddles 45 revolve they cause the body of stock adjacent to the screen to revolve along the peripheral surface of the screen and thus create a centrifugal force whichurges the pulp outwardly through the screen. As this revolving body of stock approaches any edge of the casing member 47, as for example the edge a, Fig. 8, an increased rate of outflow of the stock through the screen occurs due to the fact that the stockis being forced through a constricted area. Immediately after the stock passes the edge a, the area widens out and a reverse or inflow consequently occurswhich dislodges accumulations clinging to theinner surface of the screen.

The invention thus is applicable to a variety of forms of pulp screening machines. While I have herein shown and described preferred embodiments of my invention, it will be understood that the invention may be embodied in other forms without departing from the spirit or scope thereof.

Having thus described my invention, what I desire to claim as new is:

1. That improvement in processes of screening pulp which consists in creating a subtantial centrifugal force in the pulp in such a direction as to cause the pulp to flow along the screening surface in a generally parallel direction thereto, creating a flow of pulp through said surface to screen the pulp, maintaining the screen submerged in pulp, creating temporary reversals in the flow of pulp through the screen by gradually increasing the pressure serving to produce each reverse impulse, and terminating each impulse so produced by abruptly releasing the pressure which created it.

2. That improvement in processes of screening pulp which consists in producing the screening action by urging the pulp through a screen by centrifugal force, maintaining the screen submerged in pulp, creating abrupt temporary reversals in the flow of pulp through the screen at intervals spaced along the surface of the screen, and relatively moving the screen continuously through the regions at which such reversals are produced.

3. That improvement in processes of screening pulp which consists in creating a substantial centrifugal force in the pulp adjacent to the screening surface, causing the body of the pulp to flow along the surface of the screen in contact therewith and in a generally parallel direction thereto under the action of said force, maintaining said screen completely submerged in and under a hydraulic head of pulp while producing a flow of said pulp through said surface to screen the pulp, and creating periodic reverse impulses of the pulp through the screen substantially across the surface thereof.

4. That improvement in processes of screening pulp which consists in creating a substantial centrifugal force in the pulp adjacent to the screening surface, causing the body of the pulp to flow along the surface of the screen in contact there'- with and in a generally parallel direction thereto under the action of said force, maintaining said screen completely submerged in and under a hydraulic head of pulp while producing a flow of said pulp through said surface to screen the pulp, creating periodic reverse impulses of the pulp through the screen substantially across the surface thereof, and causing said impulses to move along the screening surface.

, 5. That improvement in processes of screening pulp which consists in creating a substantial centrifugal force in the pulp in such a direction as to cause the pulp to flow along the screening surface in a generally parallel direction thereto, creating a flow of pulp through said surface to screen the pulp, maintaining the screening surface submerged in and under a head of pulp, loosening the tailings which cling to the screen by creating abrupt and temporary reversals of the flow of pulp through the screen, and giving the tailings an ejecting movement while they are so loosened.

6. That improvement in processes of screening pulp which consists in creating a substantial centrifugal force in the pulp in such a direction as to cause the pulp to flow along the screening surface in a generally parallel direction thereto, creating a flow of pulp through said surface to screen the pulp, maintaining the screening surface submerged in and under a head of pulp, loosening the tailings which cling to the screen by creating'abrupt and temporary reversals of the flow of pulp through the screen, andv moving the material so loosened laterally along the surface of the screen. i

'7. That improvement in processesrof screening pulp which consists in flowing the pulp to be screened into the interior of a rotarycylindrical screen, urging the pulp through the screen by centrifugal force, creating said force through the motion of the screen itself, maintainingthe outer surface of the screen submerged in screened pulp, and creating inward impulses of the surrounding liquid through the screen at. spaced points in the surface thereof.

8. In a centrifugalpulp screening machine, the combination of a substantially cylindrical screen, a casing in which said screen is mounted, an inlet connection for conducting stock to be screened into said screen, an outlet connection, means cooperating with said casing to maintain the screen submerged in stock, means-for causing the stock closely adjacent to said screen to revolve along the peripheral surface of the screen, and means for acting on said revolving body of stock to create a reversal of the flow of; stock through the screening surface followed by an abrupt resumption of flow in the normal direction, said reversal occurring in a strip. of said screening surface extending longitudinally of the screen.

9. A centrifugal pulp screening machine according to preceding claim 8 in which an abrupt reversal of flow is followed by a more abrupt return to the normal direction of flow.

10. In a centrifugal pulp screening machine, the combination of a substantially cylindrical screen, a casing in which said screen is mounted, an inlet connection for conducting stock to be screened into said screen, an outlet connection, means cooperating with said casing to maintain the screen submerged in screened. stock, means for causing the stock adjacent to saidscreento revolve in a generally parallel direction to the peripheral surface of the screen whereby the centrifugal force created in said stock will cause an outflow of the stock through the screening surface, and means for acting on said revolving body of stock to create reverse impulses in the flow of stock through a portion of. said screening surface.

11. In a centrifugal pulp screening machine, the combination of a substantially cylindrical screen, a casing in which said screen is mounted, an inlet connection for conducting stockto-be screened into said screen, an outlet connection, means cooperating with said casing to maintain the screen submerged in screened stock, means for causing the stock adjacent to said screento revolve in a generally parallel directiontotlie peripheral surface of the screen whereby" the centrifugal force created in said stock will. cause an outflow of the stock through the screenings'urface, means for acting on said revolving body of stock to create reverse impulses in the flow of stock through a portion of said screening surface, to loosen coarse material clinging to the inner surface of the screen, and means inside the screen for moving the material so loosened toward one end of the screen.

12. In a centrifugal pulp screening machine, the combination of a screening drum, a casing in which said drum is mounted, means for conducting stock to be screened into said drum, an outlet connection, means cooperating with said casing to maintain said drums submerged. in

5 screened stock, means supporting said drum for rapid rotation whereby the body of liquid stock incontactwith the drum will berevolved rapidly, and meansfor acting on said revolving body of stock outside the drum to create a periodical inward movement of the stock through the screening surface of the drum.

13. In a centrifugal pulp screening machine, the combination of a screening drum, a casing in which said drum is mounted, means for conducting stock to be screened into said drum, an outlet connection, means cooperating with said casing to maintain said drum submerged in screened stock, means supporting said drum for rapid rotation whereby the body of liquid stock in contact with the drum will be revolved rapidly and said stock will flow outwardly through said screen due to the centrifugal force created in said revolving body of stock, and deflectors located closely adjacent to the outer surface of said drumand extending longitudinally thereof for acting on said revolving body of stock to create inward impulses thereof through the screen.

14. A machine according to preceding claim 13 in which said deflectors are shaped to produce a relatively gradual inward flow of the stock through the screening surface of the drum and to-cause an abrupt reversal of said flow.

15 A machine-according to preceding claim 13 in which each deflector has a surface gradually inclined with reference to the screening surface at the rearward sideof the deflector and terminating abruptly at the forward'side thereof.

16. Thatimprovement in processes of screening pulp through an approximately cylindrical screening drum which consists in causing the pulp to flow rapidly along said screening surface in a generally parallel relationship thereto and circumferentially thereof, creating a flow of pulp through said screening surface to screen the pulp, maintaining the screen submerged in pulp, and 115 causing said motion of the pulpcircumferentially of the screen to create'abrupt temporary reversals in the flow of pulp through the screening surface at intervals spaced circumferentially along said surface.

17. That improvement in processes of screening pulp through a revolving screening drum which consists in causing the pulp to flow along the revolving screening surface in a generally parallel'relationship thereto and circumferentially' thereof, creating a flow of said pulp through said surface to screen the pulp, maintaining said screening surface submerged in pulp, and causing the rotary motion of the pulp circumferentiallyof the screen to create abrupt temporary reversals'in the flowof pulp through the screen at intervals spaced circumferentially along the surface of said screen.

18'. That improvement in processes of screening' pulp through a revolving screening drum which consists incausing the pulp to flow along the revolving screening surface in a generally parallel relationship thereto and circumferentially thereof, creatinga flow of said pulp through saidsurface to screen'the pulp, maintaining said screening surface submerged in pulp, causing the rotary motion of the pulp circumferentially of the screen to create abrupt temporary reversals in the flowof pulpthrough the screen at intervals spaced circumferentially alongthe surface of said screen, and relativelymoving the screen continuously through the regionsat which such reversals are produced to traverse the reversing action. along the surface of the screen.

19. In a centrifugal pulp screening machine, 150

the combination of a screening drum, a casing in which said drum is mounted, means for conducting stock to be screened into said drum, an outlet connection, means cooperating with said casing to maintain said drum submerged in screened stock, means supporting said drum for rapid'rotation whereby the body of liquid stock in contact with the drum will be revolved rapidly and the centrifugal force so created in said body of stock will cause an outflow of the stock through the screening surface of said drum, and means providing a locally restricted area closely adjacent to the screening surface through which said revolving body of stock is caused to flow, said area being so shaped as to create a localized inward movement of the stock through said screening surface.

20. In a pulp screening machine, the combination of a substantially cylindrical screen, a casing in which said screen is mounted, an inlet connection for conducting stock to be screened into said casing, an outlet connection for discharging the screened stock from the machine, means for supporting a plurality of arms closely adjacent to the surface of the screen for rotary motion around the axis of said screen and closely adjacent to said surface, driving mechanism for revolving said arms to cause them to create a rotary motion in the stock closely adjacent to the surface of the screen, and additional means for utilizing said motion of the stock to produce temporary localized reversals of the normal flow of stock through the screening surface.

21. In a pulp screening machine, the combination of a substantially cylindrical screen, a cas ing in which said screen is mounted, an inlet connection for conducting the stock to be screened into said casing, an outlet connection for the screened stock, means cooperating with said casing to maintain said screen submerged in stock, means for supporting a plurality of arms for rotation around the axis of the screen and closely adjacent to the screening surface, driving mechanism for revolving said arms to cause them to create a similar motion in said stock, and additional means for causing said motion of the stock to create temporary reversals of the normal flow of stock through the-screening surface.

22. In a pulp screening machine, the combination of a substantially cylindrical screen, a casing in which said screen is mounted, an inlet connection for conducting stock to be screened into said casing, an outletconnection for discharging the screened stock from the machine, means for supporting a plurality of arms closely adjacent to the surface of thescreen for rotary motion around the axis of said screen and closely adjacent to said surface, driving mechanism for revolving said arms to cause them to create a rotary motion in the stock closely adjacent to the surface of the screen, and stationary members located closely adjacent to the screening surface for utilizing said motion of the stock to produce temporary localized reversals of the normal flow of stock through the screening surface.

ANTON JOSEPH HAUG. 

